Porous materials and systems and methods of fabricating thereof

ABSTRACT

A porous material with a specific surface area higher than 10/mm, and methods and system for manufacturing such a porous material. The porous material includes a plurality of pores having a substantially uniform size with a variation of less than about 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm. A system including the porous material can be configured as one of a desalination system, a super-fine bubble generation system, a capacitor system, or a battery system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority to, PCT/CN2014/089812 filed on Oct. 29, 2014, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

Porous materials such as metal foams can have high surface-area-to-volume ratios, for example described as

$\left. {s_{v} \approx {{\frac{281.8}{d}\left\lbrack {\left( {1 - \theta} \right)^{1/2} - \left( {1 - \theta} \right)} \right\rbrack} \cdot \left( {1 - \theta} \right)^{0.4}}} \right\rbrack,$

where S_(v) is the specific surface area, d is the average pore diameter in units of mm, θ is the porous ratio. For example: for a d=0.01 mm, a porous ratio of 90%, the specific surface area is 2425/mm. Porous materials can exhibit mechanical, acoustical, thermal, optical, electrical and chemical properties suitable for a variety of applications.

SUMMARY

The present disclosure relates to fabrication systems and methods for manufacturing large-dimension porous materials with high surface-area-to-volume ratios.

Typical metal forms may have pore sizes of 0.5˜8 mm. It may be possible to manufacture porous blocks with a specific surface area of 14˜3100/mm. However, the pore sizes have a large variation, for example >100%.

Some embodiments disclosed herein allow manufacturing high surface-area-to-volume ratio porous membranes with a surface area larger than 100 cm², such as 20 cm×20 cm. The sizes of the pores can be, for example, about 100 nm˜5 mm.

A fabrication system capable of fabricating large-dimension high-relative-surface-area porous materials is disclosed herein. The system can include: a colloidal particle template formation portion configured to fabricate a colloidal crystal template, an infiltration portion configured to infiltrate the colloidal particle template with an infiltrant substance, and a template removal portion configured to remove the colloidal crystal template from the infiltrant substance to obtain the macroporous material.

In some embodiments, the particle template formation portion includes an assembly apparatus configured to allow charged particles to self assemble into an array. The assembly apparatus can include: an electrophoresis tank, a DC power supply, a pump system with colloidal suspension, a reference electrode, and a working electrode, wherein an electrophoresis solution containing a suspension of template particles is disposed in the electrophoresis tank; the reference electrode and the working electrode can be vertically or horizontally arranged in the electrophoresis tank; and the working electrode provides a surface for electrophoretically fabricating the particle template. In some embodiments, the template particles are colloidal particles, and the resulting particle template is a colloidal particle template.

In some embodiments, a baking portion is further provided after the colloidal particle template formation portion, in order to dry the colloidal particle template fabricated by the colloidal particle template formation portion to thereby enhance the mechanical strength of the colloidal particle template.

In some embodiments, an uneven electrical field can be employed to fabricate a large-dimension porous material. In some embodiments, the assembly apparatus can have the reference electrode and the working electrode in a manner such that an uneven electrical field is formed between the reference electrode and the working electrode. This can be achieved by setting that the reference electrode has a dimension larger or smaller than the working electrode.

In some embodiments, the reference electrode of the assembly apparatus can have a shape of a rectangle or a round rod. The working electrode of the assembly apparatus can be a rigid planar conductor made from a metal plate, a silicon wafer, or an indium tin oxide glass (ITO) plate. In some embodiments, the working electrode can be a flexible and movable conductive tape, or conductive carbon film or carbon tube, for example for roll by roll manufacturing. The conductive tape can be, for example, an ITO tape, flexible glass with an ITO film, etc. A leak-proof inlet can be arranged on a sidewall of the electrophoresis tank such that the flexible and movable conductive tape can be fed into the electrophoresi s tank where it provides a surface to fabricate the colloidal particle template through an assembly process where the surface-charged particles deposit to form an array. The use of the flexible and movable conductive tape as the working electrode allows for a higher automation level of such a system, and the porous materials can be manufactured roll by roll.

In some other embodiments, the working electrode is not needed. For example, Sol-Gel, CVD, or PVD fabrication methods can be employed without the conductive tape or substrate, and the porous material can be fabricated slice by slice.

In some embodiments, the infiltration portion can be a physical vapor deposition apparatus, a chemical vapor deposition (CVD) apparatus, a Sol-Gel apparatus, or a chemical plating apparatus. Additionally, the infiltration portion can be an electrophoretic deposition (EPD) apparatus, which can include an EPD tank, a DC power supply, a reference electrode, and a working electrode, wherein an EPD solution can be disposed in the EPD tank; and the working electrode can be configured to carry the colloidal particle template, which further provides a surface for electrophoretic deposition of the infiltrant substance on the colloidal particle template inside the EPD tank. The DC power source can have a voltage range of about 0.01 V-500 V, with an electric field range of about 0.1-1000 V/cm. The voltage or electric field strength can be selected based on the sizes of the colloidal particles.

In some embodiments, the working electrode the EPD apparatus can be a rigid planar conductor or a flexible and movable conductive tape. In the latter case, a leak-proof inlet and a leak-proof outlet can be arranged on sidewalls of the EPD tank, which allows for leak-free feeding of the flexible and movable conductive tape into and out of the EPD tank respectively.

In some embodiments, the template removal portion can be a baking apparatus that allows the removal of the colloidal particle template from the infiltrant substance by heating. In some other embodiments, the template removal portion can be a chemical etching apparatus, which can include an etching tank with an etching solution disposed therein. The colloidal particle template can be removed by the etching solution to only keep the infiltrant substance. Additionally, if a flexible and movable conductive tape is applied in the system, the chemical etching apparatus may have a leak-proof inlet and a leak-proof outlet arranged on sidewalls of the etching tank, which allows for leak-free feeding of the flexible and movable conductive tape that carries the colloidal particle template and the infiltrant substance into and out of the etching tank respectively.

In some embodiments, the system may further include an apparatus configured to separate the infiltrant substance from the flexible and movable conductive tape, so as to obtain the porous material and recycle the flexible and movable conductive tape. For example, a blade can be disposed between the conductive tape and the porous material, and can separate the tape and the porous material, allowing the porous material to form a roll of film at a first roller, while a second roller can be employed to recycle the conductive tape.

A method of using the abovementioned system to fabricate a porous material is also disclosed herein. The method can include: step (1) using the colloidal particle formation portion to fabricate a colloidal particle template from a preparation of substantially uniformed (e.g., monosize) colloidal particles (size variations less than ±20%, such as ±10%, in terms of, for example, standard deviation); step (2) using the infiltration portion to infiltrate material into the colloidal particle template with an infiltrant substance; and step (3) using the template removal portion to remove the template and finally obtain the intact infiltrant substance as the porous material. In some cases, the template is referred to as a crystal template, because the template particles (e.g., colloidal particles) are densely packed into a crystal-like structure.

In some embodiments, the method can further include using a baking portion to dry the colloidal particle template immediately after the step (1) and before the step (2), to enhance mechanical strength of the colloidal particle template. For example, the baking temperature can be about 90-500° C., and can be adjusted based on the materials used. The relatively humidity can be >75, and the baking time can be about 0.5-2 hrs. The temperature range is selected based on the material used. For example, for PS, the annealing temperature can be about 90-100° C., and the duration can be about 30 minutes. For SiO₂, the annealing temperature can be about. 450-500° C., and the duration can be about 1.5 hr.

In some embodiments, Step (1) of the method can involve the use of the assembly apparatus as mentioned above as the particle template formation portion, in which an electrophoresis solution containing a suspension of the particles can be placed in the electrophoresis tank; the reference electrode and the working electrode can be vertically arranged in the electrophoresis tank; the reference electrode is in a shape of a round rod; the working electrode provides a surface for electrophoretically fabricating the particle template; and an electric field between the reference electrode and the working electrode is set in a range of about 0.05 V/cm-1000 V/cm.

In some embodiments, the assembly apparatus in Step (1) of the method can use an ethanol solution containing a suspension of colloidal particles such as polystyrene, SiO₂ and PMMA to electrophoretically fabricate the corresponding colloidal particle templates. Particle size can be in a range of about 100 nm-5 mm. The pH value of the ethanol solution can be in a range of about 4-9, and can be adjusted by adding NH₄OH or HNO₃. In some other embodiments, organic solvents, water, or solvent mixed with water can be used instead of ethanol.

In some embodiments, the working electrode of the assembly apparatus can be a rigid planar conductor selected from a metal plate, a silicon wafer, or an indium tin oxide (ITO) glass plate.

In some embodiments, the working electrode of the assembly apparatus can be a flexible and movable conductive tape, which can be static, or moves at a speed between 100 nm/sec and 10 cm/sec. A leak-proof inlet can also be disposed at a sidewall of the electrophoresis tank such that the flexible and movable conductive tape can be fed into the electrophoresis tank.

In some embodiments, a physical vapor deposition apparatus, a chemical vapor deposition apparatus, a Sol-Gel apparatus, or a chemical plating apparatus can be used as the infiltration portion in Step (2) to infiltrate an infiltrant substance to the colloidal particle template fabricated in Step (1).

In some embodiments, infiltration in Step (2) can be achieved using the electrophoretic deposition (EPD) apparatus as mentioned above, wherein: the EPD solution containing an infiltrant substance can be disposed in the EPD tank; the working electrode carrying the colloidal particle template can be configured to provide a surface for electrophoretic deposition of the infiltrant substance on the colloidal particle template inside the EPD tank.

In some embodiments, the working electrode of the EPD apparatus used in Step (2) can be a rigid planar conductor, or a flexible and movable conductive tape. In the latter case, a leak-proof inlet and a leak-proof outlet can be disposed at sidewalls of the EPD tank for leak-free feeding of the flexible and movable conductive tape into and out of the EPD tank respectively.

In some embodiments, the infiltrant substance used to infiltrate the colloidal particle template by the EPD apparatus in Step (2) can be a metallic ion capable of oxidation-reduction reaction, such as Ni²⁺, a ceramic such as ZnO, or a polymer. Other materials such as graphite, CeO₂, TiO₂, Cu₂O, RuO₂ can be used. Metals such as Ru, Cu, Ti, Al, Au, Ag, Pt, etc. can be used for the oxidation-reduction reactions. An ethanol solution can be used as the EPD solution. The time for the reaction can be determined based on the electric field strength, for example about 10 sec-1 hr. The pH value can be determined based on the recipe, for example, about 4-9. The solution can use IPA, ACE, etc., or organic solvents alike, so long as not causing corrosions of the colloidal particles. Water (H₂O) can also be used, but the pH value may need to be adjusted, and the electric field should not be too strong (e.g., <2.5 V/cm).

Depending on the composition of the colloidal particle template, different approaches and apparatuses may be used to remove the colloidal particle template in Step (3). In some embodiments, a baking apparatus can be used to thermally remove the colloidal particle template while still keep the infiltrant substance intact by heating the colloidal particle template carrying the infiltrant substance at about 500° C. for 1-24 hours. The materials used can be PS or PMMA. For organic materials, high-temperature removal can be used; for colloidal template made of inorganic materials such as SiO₂ or ZnO, chemical removal (e.g., BOE) can be used. In some other embodiments, a chemical etching apparatus may be used, whereby the colloidal particle template carrying the infiltrant substance can be submerged in an etching solution (e.g. 0.01-3M of ethyl acetate) disposed in an etching tank to chemically etch off the colloidal particle template while still keep the infiltrant substance intact.

In some embodiments, wherein a chemical etching apparatus is used in Step 3), a flexible and movable conductive tape carrying the colloidal particle template and the infiltrant substance can be used and be fed through the chemical etching apparatus via a leak-proof inlet and a leak-proof outlet arranged on sidewalls of the etching tank.

In some embodiments, the method can further include a step of separating the infiltrant substance from the flexible and movable conductive tape after the Step (3), to thereby obtain the porous film. For example, a separation blade can be disposed between the tape and the porous film to separate them, allowing the porous film to form a roll on the first roller, and the second roller is used to recycle the tape.

Compared with existing approaches for fabricating porous materials such as metal foams and nanoporous materials, the methods disclosed herein can have one or more of the following advantages: 1) large-dimension highly-porous materials with large relative surface areas can be achieved. The materials (e.g., porous films) can have atomic-array-like structures, with either well-ordered closely-packed pores or randomly distributed pores. In some examples, nanoporous materials that having a fine-array porous structure can be achieved.

Such fabricated highly porous materials/films can have a pore size of about 100nm-5mm, and a grain domain of about 5 μm-5 mm. The grain domains can be observed under OM as areas forming periodic or quasi-periodic structures. Defects similar to grain boundaries can exist between the grain domains. The grain boundaries between the grain domains can provide a major source of mechanical strength of the porous films.

The methods disclosed herein can be used to fabricate a large-area macroporous thin film with a dimension of >20 cm×20 cm, with a thickness of about 10 cm (depending on colloidal particle sizes), for example. A very high surface-area-to-volume ratio can be achieved, described as

$\begin{matrix} {\left. {s_{v} \approx {{\frac{281.8}{d}\left\lbrack {\left( {1 - \theta} \right)^{1/2} - \left( {1 - \theta} \right)} \right\rbrack} \cdot \left( {1 - \theta} \right)^{0.4}}} \right\rbrack,} & (1) \end{matrix}$

where S_(v) is the specific surface area, d is the average pore diameter in units of mm, θ is the porous ratio. For example: for a d=0.01 mm, a porous ratio 74%, the specific surface area can be about 4100/mm; for d=0.001 mm, the specific surface area can be about 41000/mm.

In some embodiments, a large bulk porous material with a three-dimensional (3D) structure can be manufactured. These are in contrast with the porous materials manufactured by existing approaches. Current metal foams typically have a pore size of >500 μm, and a specific surface-area of about 143100/mm, with large pore size variations (such as >100%).

The methods disclosed herein can therefore be advantageous in that the fabricated metal films can be especially suitable for catalysis and other applications where materials with large relative surface areas are needed. In addition, advantageously, some of the methods can be free from limitations of melting point of the metal/alloy used to make metal foams, and therefore can be applied to manufacturing any fine-array porous films using metal ions that are capable of oxidation-reduction reaction. Further, the metal composition in some of the fabricated metal films can reach a purity up to 99.99%, an advantage over metal foams produced by conventional manufacture processes where impurities often are introduced during metal melting. This favorable feature can also greatly increase the efficiency of catalytic reactions.

The specific areas of the porous materials (e.g., fine-array porous films) disclosed here in can be >10/mm in some embodiments, >3100/mm in some embodiments, or >4100/mm in some embodiments (such as about 4108/mm, about 8217/mm, or about 41087/mm). Meanwhile, the pores in these materials have substantially uniform sizes, such as <20% of variation in terms of standard deviation, or <10% of variation according to some embodiments.

Furthermore, some of the methods are flexible in that they allow the use of a variety of deposition/infiltration methods, such as electrodeposition, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), Sol-Gel (sol-gel process), and chemical plating (such as electroplating, electrodeposition of electro-less deposition), to infiltrate various materials, such as metals, high molecular weight polymers, and ceramics, in the fabrication of materials with macroporous structures. By readily adjusting dimensions of the particles used to make the sacrificial colloidal particle template, the fabrication of porous materials of varying pore sizes become more convenient.

By selecting assembly apparatus working electrodes with difference shapes and dimensions, materials with different shapes and sizes can be conveniently fabricated. By using a flexible and movable conductive tape, it is possible to greatly increase the automation level, and production efficiency in the process of fabricating the porous materials. The large-dimension porous materials with a closely-packed periodic fine-array porous structure according to some embodiments disclosed herein can have superb mechanical, acoustical, thermal, optical, electrical and chemical properties, and thus can be applied in various applications such as catalyst, dialysis membranes, heat exchange, energy storage, filtration, and tissue engineering.

In another aspect, an application system is provided including the porous material described above, wherein the system is configured as one of a desalination apparatus, a super-fine bubble generation system, a capacitor system, or a battery system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an OM (Optical Microscope) image of a metal foam.

FIG. 2 is a flow chart of the method to fabricate a conventional porous material.

FIG. 3 is a schematic diagram of an embodiment of the system used to manufacture a large-dimension macroporous film using a flexible and movable conductive tape as the working electrode.

FIG. 4A is a top view SEM image of a fine-array porous structure.

FIG. 4B is a side view SEM image of the structure of FIG. 4A.

FIG. 4C is another side view SEM image of the structure of FIG. 4A.

FIG. 4D is a top view SEM image of stacked nanospheres.

FIG. 4E is a low resolution (200×) top view SEM image of the inverse structure, wherein the sketches show the grain boundaries forming grain domains, which can provide mechanical strengths of the porous material.

FIG. 4F is a magnified view (500×) of the structure in FIG. 4E.

FIG. 4G is a further magnified view (2500×) of the structure in FIG. 4E.

DETAILED DESCRIPTION

Some approaches of manufacturing highly porous materials can be complex and costly, and may have difficulties producing porous materials with high purity with high specific surface areas.

FIG. 1 illustrates the microstructure of a metal foam, comprising an interconnected matrix of metallic ligaments 101 with varying lengths and orientations, and individual void spaces (pores) 100 of different shapes and sizes formed between adjacent ligaments. Typical metal foams may have pore sizes of 0.5-8 mm.

In addition to the specific area, uniformity of the pore sizes is another important factor. In the conventional metal foam illustrated in FIG. 1, the pore sizes have variations higher that 100%.

A fabrication system according to some embodiments disclosed herein can fabricate a porous material with more superior performances. The system can include a colloidal particle template formation portion configured to fabricate a colloidal particle template; an infiltration portion configured to infiltrate the colloidal particle template with an infiltrant substance; and a template removal portion configured to remove the colloidal crystal template and keep the infiltrant substance substantially intact.

FIG. 2 illustrates a process flow of manufacturing a fine-array porous material according to some embodiments using the system. The manufacture process may include: step (1), surface-charged particle deposition forming an array (assembly process), step (2), deposition/infiltration, and step (3), template removal. The system can include portions (e.g., modules) 310, 320, 330 to respectively realize these steps. A movable conductive tape can be used to transport the colloidal particle template between the waterproof inlet and outlet of each tank. Each portion can have functions as shown in FIG. 3 and as described in detail below.

FIG. 3 illustrates a system configured to fabricate large-area, fine-array porous films according to some embodiments. The system can include an electrophoresis portion 310, a deposition/infiltration portion 320, and a colloidal particle template removal portion 330.

The electrophoresis portion 310 can include an electrophoresis tank 311, a power supply 312, a reference electrode 313, a working electrode 314, a magnetic stirrer 315, a leak-proof inlet 316, and an oven/RTA 319. An electrophoresis solution 317 containing a monodispersed colloidal nanosphere suspension can be disposed in the electrophoresis tank 311; the leak-proof inlet 316 can be disposed at a side wall of the electrophoresis tank 311; the working electrode 314 can comprise a movable continuous conductive tape 318 configured to feed into the electrophoresis tank 311 via the leak-proof inlet 316, provide a surface for the formation of a colloidal particle template in the electrophoresis tank 311, move out of the electrophoresis tank 311 if the electrophoresis self-assembly of the colloidal particle template is complete, and transport the colloidal template through the oven/RTA 319 for drying.

The deposition/infiltration portion 320 can include a deposition tank 321, a power supply (not shown), a DC power source, a reference electrode 323, a working electrode 324, a leak-proof inlet 325, and a leak-proof outlet 326. An electrodeposition solution 327 can be disposed in the deposition/infiltration tank 321. The leak-proof inlet 325 and the leak-proof outlet 326 can respectively be disposed at two opposite side walls of the deposition tank 321.

The working electrode 324 can have a electrode position suspension solution 327 disposed thereover. The tape that comes from the electrophoresis portion 310 carrying the dried colloidal particle template can be fed into the deposition tank 321 via the leak-proof inlet 325. A surface for formation of a fine-array porous film over the colloidal particle template can be provided in the deposition tank 321. Upon completion of electrodeposition of the fine-array porous film, the tape can be moved out of the electrodeposition tank 321 via the leak-proof outlet 326.

The colloidal particle template removal portion 330 can include an etching tank 331, a leak-proof inlet 332, and a leak-proof outlet 333. An etching solution 334 can be disposed in the etching tank 331. The leak-proof inlet 332 and the leak-proof outlet 333 can be respectively disposed at two opposite sidewalls of the etching tank 331. The tape carrying the colloidal particle template and the fine-array porous film that comes from the deposition portion 320 can be moved into the etching tank 331 via the leak-proof inlet 332, for removal of the colloidal particle template. The tape can be moved out of the etching tank 331 via the leak-proof outlet 333 if etching of the colloidal particle template is complete. The fine-array porous film 335, referred to as the porous material or membrane of the claimed embodiments, can be separated from the movable continuous conductive tape after the tape comes out of the etching tank 331.

For example, a separation blade (not shown) can be disposed between the conductive substrate tape 337 and the porous film 335 to separate them, allowing the porous film 335 to form a roll on a first roller (not shown), and a second roller (not shown) is used to recycle the tape 337.

In some embodiments, the apparatus as shown in FIG. 3 can be used to manufacture a Nickel film with a fine-array porous structure. The process may include, for example, 1) preparation of monodispersed polystyrene (PS) colloidal suspension; 2) assembly of PS colloidal crystal template; 3) electrodeposition of Nickel; and 4) removal of PS nanosphere templates by heating or etching using ethyl acetate.

In contrast to conventional metal foams that have relatively low specific surface areas and lack of uniformity in pore sizes, the fine-array porous material has larger specific areas, and the pores therein are also highly uniform.

Table 1 below compares parameters, as defined in association with Equation (1) above, of conventional metal forms with those of the fine-array porous materials disclosed herein. As shown, the specific surface areas of the fine-array porous materials can be higher than 3130/mm, such as higher than 4100/mm. However, specific surface areas of the fine-array porous materials can also be in the range of 10/mm and 3130/mm, and would still have superb properties for various applications resulting from other properties unmatched by metal forms. For example, fine-array porous materials according to some embodiments, with a specific surface area >10/mm, can have very uniform pore sizes, such as <20% as measured by the standard deviation, or <10% as measured by the standard deviation.

TABLE 1 d Sv (mm) 281.8/d θ (1-θ){circumflex over ( )}0.5 1-Q (1-θ){circumflex over ( )}0.4 (mm2/mm3) Metal 1 281.8 0.95 0.224 0.05 0.302 14.760 Foams 0.5 563.6 0.95 0.224 0.05 0.302 29.521 0.5 563.6 0.90 0.316 0.10 0.398 48.516 0.5 563.6 0.85 0.387 0.15 0.468 62.618 0.01 28180 0.95 0.224 0.05 0.302 1476.032 0.01 28180 0.90 0.316 0.10 0.398 2425.786 0.01 28180 0.85 0.387 0.15 0.468 3130.922 Fine- 0.01 28180 0.74 0.510 0.26 0.583 4108.658 array 0.005 56360 0.74 0.510 0.26 0.583 8217.316 porous 0.001 281800 0.74 0.510 0.26 0.583 41086.578

FIG. 4A is a top view SEM image of a fine-array porous structure.

FIG. 4B is a side view SEM image of the structure of FIG. 4A.

FIG. 4C is another side view SEM image of the structure of FIG. 4A.

FIG. 4D is a top view SEM image of stacked nanospheres.

FIG. 4E is a low resolution (200×) top view SEM image of the inverse structure, wherein the sketches show the grain boudaries forming grain domains, which can provide mechanical strengths of the porous material.

FIG. 4F is a magnified view (500×) of the structure in FIG. 4E.

FIG. 4G is a further magnified view (2500×) of the structure in FIG. 4E

In some embodiments, the apparatus as shown in FIG. 3 can be used to make fine-array porous ZnO films. For example, a process can include: 1) preparation of monodispersed polystyrene (PS) colloidal suspension; 2) assembly of PS colloidal crystal template and drying of the template at about 90-100° C. in the ambient atmosphere, for example for about 30 minutes; 3) electrodeposition of ZnO in the Zn(NO₃)₂ electroplating solution with a constant electrical current (e.g. 1 mA/cm²) at about 70° C.; and 4) removal of PS nanosphere templates by heating in the ambient at about 500° C. for <2 hours. A well array prouos ZnO film with controllable periodic layers can thus be fabricated.

In some embodiments, the colloidal particle template formed by the assembly process can be made of polystyrene (PS), SiO₂, PMMA (Poly(methyl methacrylate)), or any powder substance with a sphere shape, with a particle size in the range of about 100 nm-5 mm and diameter variation (e.g., standard deviation) within about ±20%, optimally within about ±10%. For example, in an embodiment, the particle size is about 200 nm ±40 nm; in another example, the particle size is about 300 nm ±60 nm. The particles can have spherical shapes, and can be hollow or solid spheres. In some other embodiments, non-spherical shapes can be employed.

In some embodiments, the solution used has a pH value in the range of 4-9, a temperature in the range of about −10˜45° C., a DC electrical field in the range of about 0.1 V/cm-1 kV/cm, and an electrode tip withdraw velocity in a range of about 100 nm/sec-10 cm/sec.

In some embodiments, the baking temperature for the removal of colloidal crystal template can depend on the nanosphere material, and can be in a range of about ±10% of the material's glass transition temperature.

In some embodiments, the grain domain of the fine-array porous films (planar/monolithic) can be in a range of about 5 μm-5 mm, and the pore size can be in the range of about 100 nm-5 mm.

In some embodiments, the solution can have a density higher than the nanospheres, allowing the nanospheres to float on the solution. Alternatively, the solution can have a density lower than that of the nanospheres, such that the nanospheres can disperse in the solution uniformly, wherein the liquid can be specified by density.

In some embodiments, the assembly apparatus can have a vertical structure such that film thickness can be controlled, and the film can be dissembled from the apparatus.

The porous materials disclosed herein can be used in many areas of applications. For example, in some embodiments, a water purifier can employ a filter composed of a porous material of the present disclosure. The filter can be a membrane, and the high surface-area-to-volume ratio of the porous membrane as described above allows contaminated water to be purified effectively.

In some other embodiments, a salt water desalination system can be provided employing a membrane with a high surface-area-to-volume ratio. The membrane can facilitate a reverse osmosis or an ion exchange process for desalination.

In some other embodiments, a super-fine bubble generation system can be provided employing a membrane with a high surface-area-to-volume ratio. The porous structure can facilitate bubble generation in various types of liquids.

In yet some other embodiments, a capacitor or a battery can be provided employing a porous material with a high surface-area-to-volume ratio. The large surface area provided by the porous material of the present disclosure can facilitate a higher capacitance for a capacitor, or a higher rate of ion exchanges for a battery thereby improving the battery's efficiency.

In some other embodiments, the porous materials can be used in application areas such as vibration and sound absorption, impact protection, heat exchange, membranes, filtration, ion exchange, photonics, gas sensing, catalysis, biomedical engineering, etc.

Although specific embodiments have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects described above are not intended as required or essential elements unless explicitly stated otherwise. Various modifications of, and equivalent acts corresponding to, the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of the present disclosure, without departing from the spirit and scope of the disclosure defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures. 

1. A porous material with a specific surface area higher than 10/mm, the specific surface area depending on different pore sizes, wherein the porous material comprises a plurality of pores having a substantially uniform size with a variation of less than about 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm.
 2. The porous material of claim 1, wherein the porous material is substrateless membrane.
 3. The porous material of claim 1, comprising a plurality of grain boundary regions filled with a solid material to increase a mechanical strength of the porous material, wherein the specific surface area is higher than 4100/mm, wherein the size variation is less than about 10%, and wherein the grain boundary regions have a size of about 5 μm-15 cm.
 4. A system configured to fabricate a porous material, the system comprising: a particle template formation portion configured to fabricate a particle template; an infiltration portion configured to infiltrate the particle template with an infiltrant substance, and a template removal portion configured to remove the particle template and keep the infiltrant substance substantially intact, to thereby form a sub strateless porous material with a specific surface area higher than 10/mm, wherein the porous material comprises a plurality of pores having a substantially uniform size with a variation less than 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm.
 5. The system of claim 4, further comprising a baking portion configured to dry the particle template fabricated through the particle template formation portion to thereby enhance mechanical strength of the colloidal particle template.
 6. The system of claim 5, wherein the particle template formation portion comprises an electrophoresis assembly apparatus including: an electrophoresis tank; a DC power supply; a magnetic stirrer; a reference electrode; and a working electrode; wherein: an electrophoresis solution containing a suspension of particles is disposed in the electrophoresis tank; the reference electrode and the working electrode are substantially vertically arranged in the electrophoresis tank; and the working electrode provides a surface for electrophoretically fabricating the particle template.
 7. The system of claim 6, wherein the reference electrode has a shape of a round rod and is disposed adjacent to an air-liquid interface or lower than the interface by about 0-5 cm.
 8. The system of claim 7, wherein the working electrode comprises a flexible and movable conductive tape, and a leak-proof inlet is arranged on a sidewall of the electrophoresis tank such that the flexible and movable conductive tape can be fed into the electrophoresis tank.
 9. The system of claim 4, wherein the infiltration portion comprises an electrophoretic deposition (EPD) apparatus including: an EPD tank; a DC power supply; a reference electrode; and a working electrode; wherein: an EPD solution is placed in the EPD tank; and the working electrode is configured to carry the colloidal particle template, the colloidal particle template providing a surface for electrophoretic deposition of the infiltrant substance on the colloidal particle template inside the EPD tank.
 10. The system of claim 4, wherein the template removal portion comprises a chemical etching apparatus including an etching tank having an etching solution disposed therein, whereby the particle template is removed by the etching solution to only keep the infiltrant substance.
 11. The system of claim 10, wherein a leak-proof inlet and a leak-proof outlet are arranged at sidewalls of the etching tank for leak-free feeding of a flexible and movable conductive tape carrying the colloidal particle template and the infiltrant substance into and out of the etching tank, respectively.
 12. The system of claim 11, further comprising a blade configured to separate the infiltrant substance from the flexible and movable conductive tape to obtain the porous material and to recycle the flexible and movable conductive tape.
 13. A method of fabricating a porous material, comprising: (1) fabricating, with a particle template formation portion, a particle template; (2) infiltrating, with an infiltration portion, the particle template with an infiltrant substance; and (3) removing, with a template removal portion, the particle template and keep the infiltrant substance intact to thereby form a substrateless porous material with a surface-area-to-volume ratio higher than about 10/mm, wherein the porous material comprises a plurality of pores having a substantially uniform size with a variation of less than about 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm.
 14. The method of claim 13, further comprising baking the particle template immediately after the step (1) and before the step (2) to enhance mechanical strength of the particle template, wherein said baking is performed at a temperature of about 90-500° C., a relative humidity of >75, for a duration of about 0.5-2 hrs.
 15. The method of claim 14, wherein: an electrophoresis solution containing a suspension of colloidal particles is disposed in an electrophoresis tank; a reference electrode and a working electrode are substantially vertically disposed in the electrophoresis tank; the reference electrode has a shape of a round rod; the working electrode provides a surface for electrophoretically fabricating the particle template; and an electric field between the reference electrode and the working electrode is in a range of about 0.1 V/cm-1000 V/cm.
 16. The method of claims 15, further comprising providing the suspension of particles including a powder substance selected from at least one of polystyrene, SiO₂, or PMMA, wherein the power substance has a particle size of about 100 nm-5 mm, and wherein the electrophoresis solution comprises an ionic solution configured to provide electrical charges to surfaces of the colloidal particles.
 17. The method of claim 16, wherein the electrophoresis solution comprises at least one of: an ethanol solution with a pH value of about 4-9, NH₄OH/HNO₃, or SDS.
 18. The method of claim 17, wherein the working electrode is static or configured to move at a speed of about 100 nm/sec-10 cm/sec.
 19. The method of claim 13, further comprising heating the particle template carrying the infiltrant substance to about 500° C. for less than 24 hours to thereby thermally remove the colloidal particle template while keeping the infiltrant substance substantially intact and oxidizing metal structure surfaces, wherein the particle template comprises polymers.
 20. The method of claim 14, further comprising chemically removing the particle template while keeping the infiltrant substance substantially intact and avoiding oxidizing metal structure surfaces, and wherein said chemically removing comprises etching at a temperature of about 40-80° C. for about 1-4 hours. 